Final answer:
The patient was admitted to the acute care setting for excisional debridement of a decubitus stage 3 ulcer on their right heel.
Step-by-step explanation:
The reason for admitting the 77-year-old nursing home patient to the acute care setting was the excisional debridement of decubitus stage 3 ulcer of the right heel. Decubitus ulcers, also known as bedsores, are caused by constant pressure on bony body parts, leading to tissue death. In this case, the patient had a stage 3 ulcer on their right heel, which required surgical removal of necrotized tissue to prevent further complications.